组合模式

 需求中是体现部分与整体层次的结构时，以及你希望用户忽略组合对象与单个对象的不同，统一的使用组合结构中的所有对象时，

就应该考虑组合模式了

代码如下：

public abstract class Component {
    protected String name;

    public Component(String name) {
        super();
        this.name = name;
    }
    
    /**通常都用add和remove方法来提供增加或移除树叶或树枝的功能*/
    public abstract void add(Component com);
    public abstract void remove(Component com);
    public abstract void display(int depth);
    
}

public class Leaf extends Component{

    public Leaf(String name) {
        super(name);
    }

    /**
     * 由于叶子没有增加分枝和树叶，所以add和remove方法实现没有意义，
     * 但是这样可以消除叶节点，和枝节点在抽象层次的区别，它们具有完全一致的接口
     */
    @Override
    public void add(Component com) {
        System.out.println("Leaf no add");
    }

    @Override
    public void remove(Component com) {
        System.out.println("Leaf no remove");
    }

    @Override
    public void display(int depth) {
        System.out.println(String.valueOf(depth)+"----name----"+name);
    }

}

import java.util.ArrayList;
import java.util.List;

public class Composite extends Component {
    private List<Component> children = new ArrayList<Component>();
    public Composite(String name) {
        super(name);
    }

    @Override
    public void add(Component com) {
        children.add(com);
        
    }

    @Override
    public void remove(Component com) {
        children.remove(com);
        
    }

    @Override
    public void display(int depth) {
        System.out.println(String.valueOf(depth)+"----name----"+name);
        for (Component comp : children) {
            comp.display(depth+2);
        }
        
    }

}

public class CompositeTest {

    public static void main(String[] args) {
        //生成树根 root 长出叶子：Leaf A,Leaf B
        Composite root = new Composite("root");
        root.add(new Leaf("Leaf A"));
        root.add(new Leaf("Leaf B"));
        
        //长出分枝Composite X ,Composite X上长出叶子：Leaf XA,Leaf XB
        Composite comp = new Composite("Composite X");
        comp.add(new Leaf("Leaf XA"));
        comp.add(new Leaf("Leaf XB"));
        root.add(comp);
        
        //长出分枝Composite Y ,Composite Y上长出叶子：Leaf YA,Leaf YB
        Composite comp2 = new Composite("Composite Y");
        comp2.add(new Leaf("Leaf YA"));
        comp2.add(new Leaf("Leaf YB"));
        root.add(comp2);
        
        root.add(new Leaf("Leaf C"));
        Leaf leaf = new Leaf("Leaf D");
        root.add(leaf);
        root.remove(leaf);
        
        root.display(1);
    }

}

结果：

1----name----root
3----name----Leaf A
3----name----Leaf B
3----name----Composite X
5----name----Leaf XA
5----name----Leaf XB
3----name----Composite Y
5----name----Leaf YA
5----name----Leaf YB
3----name----Leaf C